The present invention relates to a polyurethane/polyisocyanurate foam having improved adhesion properties. It relates further to its use in the production of metal composite elements, to metal composite elements produced therewith, and to a process for the production of the metal composite elements.
Metal sandwich elements based on rigid polyurethane (PU) foams, that is to say both rigid polyurethane (PUR) and rigid polyisocyanurate (PIR) foams, play an important role in the construction of industrial buildings. In addition to the heat insulation and fire behaviour, the bond properties, in particular the adhesiveness at the foam/steel interface, play an important role. The adhesiveness of the metal facing to the PU foam is particularly important for the continuous manufacture of such elements.
The processing of PIR foams in particular is conventionally carried out with the addition of adhesion promoters, 2K polyurethane adhesion promoter systems especially having become established. The adhesiveness is in principle markedly improved by the use of such 2K adhesion promoter systems. For the manufacturer of the finished components, this means an improvement in the product in that the long-term risks of adhesion failure are massively reduced.
In this connection, EP 1 516 720 A1 discloses the use of a polyurethane adhesion promoter for improving the adhesion between the layers of a composite element containing a polyisocyanurate foam and facings, as well as the composite elements as such and a process for their production. The adhesion promoter used is a polyurethane-based adhesion promoter known from the prior art having a density of from 400 to 1200 g/l. This adhesion promoter is generally obtainable by reacting polyisocyanates with compounds having two isocyanate-reactive hydrogen atoms, the reaction ratio being so chosen that the ratio of the number of isocyanate groups to the number of isocyanate-reactive groups in the reaction mixture is from 0.8 to 1.8:1, preferably from 1 to 1.6:1. Preferred embodiments relate to the use of reactive 2K polyurethane adhesion promoter, which is still reactive when the foam layer and the facing are brought together. However, this involves a potential risk to users.
In general, the use of such adhesion promoters means additional costs for material and processing technologies. Moreover, difficulties with adequate homogenisation of the adhesion promoter components can occur in the processing of such 2K adhesion promoter systems. Insufficient homogenisation can represent a high risk in respect of the long-term bond properties of the metal composite elements. Failure of the adhesion of the facing to the foam can occur in the case of fluctuating temperatures. Furthermore, the processing of a 2K adhesion promoter system means relatively high rejections of chemical raw materials and steel sheets at the beginning of a production phase.
PIR foams which, on processing to metal composite elements, exhibit good adhesiveness in the foam/sheet metal composite even without being pretreated with adhesion promoter would therefore be desirable. In particular, a PIR foam which exhibits good adhesiveness in the continuous manufacture of metal composite elements even at comparatively low twin-belt conveyor temperatures would be desirable.